This invention relates generally to a multi-gradation display for displaying images, such as letters, patterns, etc., and more particularly to a method for controlling the display of images in multi-gradations by activating a selected number of dots or pixels in a plurality of defined dot submatrices which together comprise the entire image display, e.g., an active matrix display panel.
One example of devices which can display images in multi-gradations are liquid crystal display (LCD) panels, which devices are employed as displays for televisions, personal computers and the like. In these LCD panels, gray scale gradations may be realized in the following manner. First, in order to display an image on a display panel in multi-gradations, different gradations are created by activating, in each of a plurality of predefined submatrices or subgroups, a selected or predetermined number of n dots in the horizontal direction of the display panel. Thus, the defined submatrices together, in a tiled-like screen fashion, comprise the entire dot matrix display body for displaying an image. The positions of these activated dots throughout each submatrix, i.e., those selected dots in a defined submatrix turned on in response to received data signals, are changed to new positions in each submatrix per frame of the dot matrix display. It is conventional practice to apply a cycle of vertical occurrences of activated dots in each submatrix whose positions are changed from frame to frame, which change is the same for every gradation, e.g., the same n dots are sequentially activated in different horizontal rows of each defined submatrix. In other words, in an n dots by n dots submatrix or subgroup, line groups of activated dots within the respective submatrix may be shifted vertically up or down and/or horizontally right or left in sequential frames to thereby enable different levels of gradation and provide multi-gradation displays of an image. This conventional practice is explained now in further detail with reference to FIG. 1.
FIGS. 1A and 1B illustrate a single 8 dot by 8 dot defined submatrix in a larger active matrix LCD panel. In FIG. 1A, in a first applied frame, all the dots in the first horizontal row of the submatrix, indicated as circles, are activated. In the next or second frame, all the dots, indicated as triangles in the eighth horizontal row of the submatrix, are activated. Then, in the third frame, all the dots, indicated by crosses in the seventh horizontal row of the submatrix, are activated and so on. As a result, all of the respective 8.times.8=64 dots become activated once in the first to eighth frames of the dot matrix display and the display is characterized as being of 1/8 gradation. In the example of FIG. 1B, the distributions of the activated dots in the several respective dot matrix frames are sequentially applied as different spatial oblique rows across the submatrix. This example is also characterized as being of 1/8 gradation.
These prior art matrix displays, however, have disadvantages in that, when a gradation image occupies an area on an LCD panel larger than an n by n dot defined submatrix, fringes occur. Also, when the gradation image occupies an area on an LCD panel smaller than an n by n dot defined submatrix, the activated dots interfere with one another with a result that more conspicuous fringes occur which are sensed by and disturbing to the naked human eye. The fringes become especially objectionable and disturbing when tiling patterns are created between different types of gradations.
On the other hand, Tateuchi et al. described in Japanese Patent Laid-Open Publication No. 287828/1988 an LCD driving method in which the positions of selective dots, which are activated in the same phase, are in scattered locations of a display panel in order to prevent display flickering. It is difficult, however, to employ this particular approach for the purpose of preventing activated dot interference which produces fringes and results in an unsatisfactory multi-gradation display.
It is, therefore, an object of this invention to provide an improved multi-gradation display.
It is another object of this invention to provide a display control method for a multi-gradation image display which is substantially free from the above mentioned disadvantages.
It is a further object of this invention to provide a display having gray scale capability that is substantially free of interference annoyance perceptible to the naked human eye.
It is another object of this invention to provide a multi-gradation display which will exhibit easily discernable images without the experience of objectionable fringes.